No, he didn't. He took on Earth's heroes. X-Men, FF, Avengers, Hulk, etc.
I have no idea why the Pantehon of Earth Gods didn't get involved. Needless to say, if Onslaught even looked at Galactus wrong, he'd be killed with little to no effort.
I'd say it would be bad news for Onslaught if Quasar, Surfer, Warlock/The Watch (Gems and all), Thor (who was absent for most of the Onslaught saga) and the likes showed up.
True, the DC universe contains a lot of characters that, in terms of pure power, are often matches for those found in the marvel universe. Wonder Women and Superman alone spring to mind. Also, as there are few mutants in the DC universe one imagines Onslaught would have a harder time possessing the heroes.